I can’t get over the age gap

dinner: oreo ice cream sandwich😋 I (19f) met my friends cousin (28m) on a night out drinking. We all got quite drunk and one thing led to another and we made out… a lot. Forward to the next day and he ask my friend for my number and we start texting. Pretty shortly after we meet up and spend the day together. We’ve met up a few times now and it’s always been fun but, like the title says, i just can’t get over the age gap. I’m 19 (turning 20 this year), i’m dropping out of college and starting an apprenticeship this september. I’m insecure, struggle with acne, all things typically 19. Hes 28, has a stable job, has an apartment, car,… is basically a fully established adult. It just feels like we’re on different levels in life, because well, we are! My parents know there’s “a guy” and that he’s my friends cousin but they don’t know his age. I haven’t even really told my friends about him because I can’t get over the fact that he’s 8 years older than me. I’m usually very open and not one to keep secrets from my family and friends but this just feels like something i can’t talk about because it will raise eyebrows, rightfully so. When I talk to him about it, that I can’t get over the age difference he always says that we always “think too much” and that there are “bigger things to worry about”. “It doesn’t have to be weird if we don’t make it weird”. Maybe I am being too rational about this but I just know, if I saw a 19 year old dating a 28 year old, I would be extremely weirded out. Deep down I know I can’t confidently say “look this is the guy i’m seeing and he’s 28”. That’s not fair to me nor to him. He should have someone who isn’t going to be embarrassed to have him as a boyfriend. Also, if i’m being honest with myself, I don’t even really want a boyfriend no matter the age or whatever. I still feel like a child and want to live life and get to know myself and explore who and what I am. He’s already been through this phase. He tells me he hast been this “emotionally open” with someone in a long time which makes me feel bad for thinking of leaving him. In my gut I just know that I can’t and won’t start a real, official relationship with him because just no. I guess I already answered for myself that I’m going to end this relationship. Now i’m asking for advice I suppose on how to let him down gently. Like I mentioned he is quite emotionally invested. If it weren’t my friend’s cousin (we’ve been friends for almost 15 years), it would be much easier. All kinds of advice and input would be appreciated. Thank you!!!